I excluded ALT (binoculars trigger bug) and the (quite trivial)
trigger bug that triggers the bonus level from the very beginning of the
game.
Comments on part 2:
There are 3 SLs (save-loads). They all have specific functions
besides segmentation. The SLs at 18s and 1m13s remove the fire from
Lara's body. I don't know why. The SL at 2m04s cancels the rest of the
fly-by. We need to wait for the gate to open before we cancel the fly-by.
The flare-wall bug at 54s is the key shortcut of the game. All other
bugs can be replaced by some not-too-long glitchless routes.
Comments on part 3:
The SL at 2m29s has specific functions besides segmentation. It
resets the animations of the spiked rollers. It's essential. Only a good
reset can push Lara correctly.
The IGT of the last save (at the beginning of CIL1, 2nd visit) is
5m48s433ms. The rest of the game has to be timed manually. The final IGT
is 6m56s567ms.